Estimation of conectration of free Chloring in pool water using a comparator

How does chlorine help kill microorganisms in water?

• chlorine reacts with water to form a weak acid called hypochlorous acid

• this dissociates into H⁺ ions and hypochlorite ions, which have little power to kill germs

• the hypochlorous acid needs to be kept in its associated form in order to be effective

What is the main chemical added during the comparator test?

DPD

What colour is DPD?

pink

What test kit is used in this experiment?

Hach test kit

Describe the method used to measure the concentration of free chlorine in pool water:

• small quantity of deionised water placed in one viewing tube - reference tube - and placed on the left in the black comparator box

• small quantity of water sample placed in another viewing tube tube, a DPD tablet is added and sol. is stirred until dissolved

• a pink colour is observed due to the presence of free chlorine

• this placed on the right in the black comparator box

• comparator box is held up to a source of light + the disc is rotated until the colours in each openeing best match each other

• the number visible is recorded in ppm

• cover is placed over the colour disc to prevent discolouration from age and use